We selected patients who performed CTA examination of both lower limbs because of trauma or tumor of unilateral lower extremity in Xi'an honghui hospital from July 2017 to June 2018. All CT data were available on the digital image archive system PACS(Picture Archiving and Communications Systems, Synapse, Fujifilm Inc., Tokyo Japan). The study protocol was approved by the Hospital Ethics Committee. Inclusion criteria were as follows: 1. CT scan with a direction perpendicular to lower limbs; 2. at least one side of lower limb without fracture or tumor; 3. no obvious flexion, varus and valgus deformity in bilateral knees; 4. no obvious degeneration in bilateral knees. Exclusion criteria were as follows: 1. both lower limbs have fracture, residual internal fixation, tumor and other pathological changes; 2. 3D reconstruction showed incomplete extension of both knee joints or hip joints; 3. obvious deformity of external tibial arch.
Transverse CT scans (SOMATOM Definition, Siemens Inc, Munich, Germany) were made with 1-mm thickness and 1 mm interval ranging from lumbar 4/5 intervertebral space to sole of foot, including the entire lower extremity. The patient was in supine position with both lower limbs straight.
All measurement was done with PACS:
Three-dimensional reconstruction of CT data were performed and the following marks were made: 1. medial edge of patellar tendon 8 mm distal to lateral tibial plateau,2. the medial and lateral border of the patellar tendon at the tibial attachment, connecting the two points. 3. the medial and lateral border of the widest part of the tibial tubercle, connecting two points. 4.The proximal and distal ends of the sharp margin of the anterior tibial crest were marked, two points between them were also marked on the anterior tibial crest, making the distance trisection(Fig. 1).
Finally, 122 patients with 122 lower extremities were included in this study, There were 89 males and 33 females with a mean age of 51.4 years (18–81 years), including 67 left lower extremities and 55 right lower extremities.
The following marks and measurement were made on CT axis scans:
1.the angle between PACS transverse axis and the surgical epicondylar axis(SEA), which was determined for connecting the most prominent points of the lateral epicondyle and the deepest point of the sulcus on the medial epicondyle of the femur(Fig. 2). 2. the angle between PACS longitudinal axis and the line connecting the middle of the PCL and medial border of the patellar tendon (MEPT) at the level 8 mm distal of the lateral tibial joint surface(Fig. 3). 3. the angle between PACS transverse axis and the transverse axis of the tibia (TAT)at the level 8 mm distal of the lateral tibial joint surface(Fig. 4). 4. the angle between PACS longitudinal axis and the line connecting the projected middle of the PCL and medial border of the patellar tendon at the tibial attachment (Akagi line), and the angle between PACS longitudinal axis and a line connecting the projected middle of the PCL and the medial 1⁄3 of the patellar tendon(M1/3) at the patellar tendon attachment level(Fig. 5). 5. the angle between PACS longitudinal axis and the line connecting the projected middle of the PCL and medial border of tibial tubercle (MBTT), and the angle between PACS longitudinal axis and a line connecting the projected middle of the PCL and the medial 1⁄3 of tibial tubercle (Insall line) (Fig. 6). 6. the angles between PACS longitudinal axis and the line connecting the four points on the anterior tibial crest (ATC1-4) and projected middle of the PCL respectively (Fig. 7–10).
The measurement data were divided into 10 groups according to 10 axes of tibia, which were Akagi line group, Insall line group, MEPT axis group, M1⁄3 axis group, TAT axis group, MBTT axis group, ATC1 axis group, ATC2 axis group, ATC3 axis group and ATC4 axis group. According to the principle that the longitudinal and transverse axes of PACS in each scanning plane of CT is identical, the angle between SEA and TAT as well as the angles between the perpendicular to SEA and the other nine axes was calculated. Compared with SEA or the perpendicular to SEA, the external rotation was positive and the internal rotation was negative.
After three weeks, 20 randomly selected CT scans were measured again by the same author (Observer I) and another author (Observer II) who conducted an independent evaluation to determine intra- and interobserver variability. A conclusion was made: an intraclass correlation coeffcient (ICC) > 0.8 was considered excellent agreement, ICC 0.6–0.8 was fair to good agreement, and ICC < 0.6 was poor agreement.
Quantitative data was expressed as means ± standard deviation (SD). Statistical analyses were performed with PASW statistics 18 (SPSS Inc., Chicago, IL, USA). The normality assumption of our data was checked by the Kolmogorov-Smirnov test. Single factor ANOVA and paired t-test were used to compare data between 10 axes. Values of P < 0.05 were considered significant.